Traditionally, mechanical equipment such as engines and machines encased by a housing have been maintained by regular maintenance schedules. In the event of a malfunction, an operative or engineer will run the machine or engine through a series of test functions in a trouble-shooting programme and note the reaction of the machine or engine to each test function. From observation of the action or reaction of the machine or engine to a given function, it is possible to diagnose, at least in part, the general area of malfunction of the machine. Thereafter the machine is dismantled to an extent sufficient to examine the possible malfunction and to repair the fault.
Such activity is time-consuming and on many occasions the trouble-shooting programme or the number of available diagnostic functions for the machine is insufficient to pin-point with accuracy the precise location of the fault. On many occasions a machine or engine will need to be partially dismantled involving much wasted effort, particularly when the trouble-shooting regime or programme gives an false indication of a fault.
Hitherto, detailed inspection of machines or engines has involved the determination of changes in sound, the use of ultrasound examinations for cracks and breaks in equipment and also for x-ray analysis of particular components. In each case, however, these techniques only serve to assist in diagnosis of faults. Where the components concerned are readily accessible or where the machine has been partially dismantled, only then can examination of individual suspect components be undertaken.
In complex machines such as steam or gas turbine engines and the like, there is a need to determine faults in machine and to locate, with precision, the area of the fault before commencing stripping of the engine to examine the faulty component(s) closely for repair/replacement.
In medical science, it has, for many years, been the practice to use endoscopes to examine body cavities sometimes at quite significant distances from the point of access. An endoscope may typically have an examination light source and an optical receiving device at the distal end of a flexible support arm. It is entered into a body orifice and entry is continued until examination of the desired area of disease/damage is reached for internal examination. The flexible support arm is capable of adopting a serpentine path to follow the path of the body orifice. Thus, the walls of the body orifice serve to guide the endoscope and assist the endoscope in following its serpentine path. The use of endoscopes for the examination of machines and engines has been used with some degree of success. A major difficulty of such devices, however, is the problem of controlling the endoscope within the machine and arranging for the light and optical sensor to be disposed in the correct area of the machine for examination. Where the point of examination of the machine is near an access port then endoscopes have been fairly successful in the internal examination of complex machinery. Likewise, where the repair is similarly located near an access port and is a simple repair, for example, such as tightening a screw or grinding a metal surface then a working device such a borescope may be used.
A typical prior art proposal is set out in British Patent Specification No 2033973 which relates to a method of inspecting a gas turbine engine, which latter has a casing provided with at least one access aperture to allow inspection of engine components located within the casing the method comprising inserting guide means into the access aperture locating one end of the guide means being external of the casing and the other end of the guide means being located adjacent the engine component to be inspected fixing the guide means in said location and inserting a flexible endoscope or other remote viewing inspection apparatus into the guide means. In this case the guide means serves as the guide for the flexible endoscope rather in the manner of the body orifice described above.
In European Patent Specification No 0907077 there is described and claimed a method and apparatus for inspecting in situ a turbine engine blade in a stage of a gas turbine engine by using eddy currents, which examination is effected from a remote location. The engine includes a casing about the stage of the engine to be examined and a borescope hole which extends through the casing and into the stage in which the turbine blade in question is located. The turbine blade may be inspected by inserting the apparatus through the borescope hole in the turbine casing. In this case the essence of the invention is the use of the sensor probe means for holding eddy current coils and for sensing imperfections in the structure detected by induced eddy currents within the component, such as a turbine blade, being examined.
U.S. Pat. No. 5,644,394 relates to a system for repairing damaged airfoils for gas turbine engines including a plurality of rigid attachment tools. Each attachment tool is individually shaped to access a leading edge of a damaged airfoil of a particular stage of a gas turbine engine. The attachment tools enable repair of damaged airfoils without dissembling the gas turbine engine. In this case, however, the tools are rigid and are designed to operate juxtaposed the borescope opening into the engine housing.
British Patent Specification No 2154335 relates to a technoscope for internal inspection of a power plant such as an aircraft power unit equipped with noncircular preferably cornered, e.g. square, wall ports comprising a first rigid guide shaft of non-circular cross-section insertible into one of the wall ports and having a lateral distal outlet and a guiding element which passes through said first guide shaft and has a flexible distal portion an intermediate portion of its cross section matches that of the first guide shaft and a proximal control system for control deflection of said flexible distal end the guiding element is used to guide a flexible endoscope shaft to the desired site within the plant to be inspected. Again, a rigid guide shaft is used for insertion into a wall port and serves to provide support for a flexible guiding element which passes through said guide shaft as a sliding fit.
U.S. Pat. No. 5,803,680 also relates to an instrument such a technoscope for machining the surfaces of engine blades in normally inaccessible cavities having a machining tool able to be simultaneously observed at a machining location with an optic comprising an instrument shank to which the head is distally coupled, said head carrying the tool and being pivotable relative to the longitudinal axis of the instrument shank. In order to create the possibility of being able to measure damage to the surface to be machined with this instrument, a measuring tool with a measuring template is attached to the instrument head and when this instrument head is pivotable into the field of view of the optic the measuring tool may be attached to the head of instrument in a simple manner instead of a machine tool.
From the foregoing, therefore, it will be appreciated by a person skilled in the art, that there is a need for an internal examination and repair function without disassembling the machine or engine. It will be obvious to the person skilled in the art that maintenance carried out in this way has the considerable advantage of saving of time effort and cost by being able to effect a repair or an inspection without dismantling the engine or machine into its component parts.
The prior art, however, all suffers from the problem that in order to work on or examine a component or part, the area to be worked upon or the site to be observed, needs to be near the access port for the technoscope, borescope or endoscope as the case may be, or guide means must be provided to support the endoscope/borescope during its passage to the area of work/examination.
There is, therefore, a need for apparatus to inspect and/or work on a component of an engine which is more remote from the access port and where the access path is convoluted.